Diffusion tensor tractography (DTT) is known to be useful in detecting white matter lesions. In the current study, we report on two hemiparetic patients with risk factors who showed abnormalities of the corticospinal tract (CST) on diffusion tensor tractography (DTT) prior to the manifestation of hemiparesis. Two hemiparetic patients with risk factors (preterm, low birth weight) and six age-matched normal control subjects were enrolled to this study. Diffusion tensor imaging (DTI) was performed at the age of 43 weeks (patient 1) and 33 weeks (patient 2) using 1.5-T with a Synergy-L Sensitivity Encoding (SENSE) head coil. We measured fractional anisotropy (FA), apparent diffusion coefficients (ADCs), and fiber counts of the CST. There were no definite asymmetric findings on physical examination and conventional brain MRI. By contrast, DTT showed a unilateral CST disruption at the periventricular white matter, low FA values, and low CST fiber counts compared with those of the unaffected CST and controls. These patients were diagnosed with hemiparetic cerebral palsy when we re-evaluated these patients at the age of 6 years (patient 1) and 3 years of age (patient 2), respectively. In these two patients, DTT revealed abnormalities of the CST prior to the manifestation of hemiparesis. Therefore, it seems that DTT would be a useful modality in detecting CST abnormalities in advance of clinical manifestation in infants with high risk factors.